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Opitz A. Energy level alignment at planar organic heterojunctions: influence of contact doping and molecular orientation. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:133001. [PMID: 28195076 DOI: 10.1088/1361-648x/aa5a6c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Planar organic heterojunctions are widely used in photovoltaic cells, light-emitting diodes, and bilayer field-effect transistors. The energy level alignment in the devices plays an important role in obtaining the aspired gap arrangement. Additionally, the π-orbital overlap between the involved molecules defines e.g. the charge-separation efficiency in solar cells due to charge-transfer effects. To account for both aspects, direct/inverse photoemission spectroscopy and near edge x-ray absorption fine structure spectroscopy were used to determine the energy level landscape and the molecular orientation at prototypical planar organic heterojunctions. The combined experimental approach results in a comprehensive model for the electronic and morphological characteristics of the interface between the two investigated molecular semiconductors. Following an introduction on heterojunctions used in devices and on energy levels of organic materials, the energy level alignment of planar organic heterojunctions will be discussed. The observed energy landscape is always determined by the individual arrangement between the energy levels of the molecules and the work function of the electrode. This might result in contact doping due to Fermi level pinning at the electrode for donor/acceptor heterojunctions, which also improves the solar cell efficiency. This pinning behaviour can be observed across an unpinned interlayer and results in charge accumulation at the donor/acceptor interface, depending on the transport levels of the respective organic semiconductors. Moreover, molecular orientation will affect the energy levels because of the anisotropy in ionisation energy and electron affinity and is influenced by the structural compatibility of the involved molecules at the heterojunction. High structural compatibility leads to π-orbital stacking between different molecules at a heterojunction, which is of additional interest for photovoltaic active interfaces and for ground-state charge-transfer.
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Neo WT, Li X, Chua SJ, Ling Chong KS, Xu J. Enhancing the electrochromic performance of conjugated polymers using thermal nanoimprint lithography. RSC Adv 2017. [DOI: 10.1039/c7ra08850g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Thermal nanoimprinting is employed to create nanopatterned electrochromic conjugated polymer films, giving superior color-changing properties compared to a reference device.
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Affiliation(s)
- Wei Teng Neo
- Institute of Materials Research and Engineering
- A*STAR (Agency for Science, Technology and Research)
- Singapore 138634
- NUS Graduate School for Integrative Sciences and Engineering
- National University of Singapore
| | - Xue Li
- Institute of Materials Research and Engineering
- A*STAR (Agency for Science, Technology and Research)
- Singapore 138634
| | - Soo-Jin Chua
- Institute of Materials Research and Engineering
- A*STAR (Agency for Science, Technology and Research)
- Singapore 138634
- Department of Electrical and Computer Engineering
- National University of Singapore
| | - Karen Siew Ling Chong
- Institute of Materials Research and Engineering
- A*STAR (Agency for Science, Technology and Research)
- Singapore 138634
| | - Jianwei Xu
- Institute of Materials Research and Engineering
- A*STAR (Agency for Science, Technology and Research)
- Singapore 138634
- Department of Chemistry
- National University of Singapore
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3
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Jacobs IE, Aasen EW, Nowak D, Li J, Morrison W, Roehling JD, Augustine MP, Moulé AJ. Direct-Write Optical Patterning of P3HT Films Beyond the Diffraction Limit. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29. [PMID: 27740691 DOI: 10.1002/adma.201603221] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2016] [Revised: 08/01/2016] [Indexed: 05/02/2023]
Abstract
Doping-induced solubility control is a patterning technique for semiconducting polymers, which utilizes the reduction in polymer solubility upon p-type doping to provide direct, optical control of film topography and doping level. In situ direct-write patterning and imaging are demonstrated, revealing sub-diffraction-limited topographic features. Photoinduced force microscopy shows that doping level can be optically modulated with similar resolution.
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Affiliation(s)
- Ian E Jacobs
- Department of Materials Science and Engineering, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
| | - Erik W Aasen
- Department of Chemical Engineering, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
| | - Derek Nowak
- Molecular Vista, Inc, 6840 Via Del Oro, Suite 110, San Jose, CA, 95119, USA
| | - Jun Li
- Department of Chemical Engineering, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
| | - William Morrison
- Molecular Vista, Inc, 6840 Via Del Oro, Suite 110, San Jose, CA, 95119, USA
| | - John D Roehling
- Department of Chemical Engineering, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
| | - Matthew P Augustine
- Department of Chemistry, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
| | - Adam J Moulé
- Department of Chemical Engineering, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
- Department of Chemistry, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
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4
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Iida T, Yasuda M, Kawata H, Hirai Y. Study on Induced Stress and Strain in Direct Nanoimprint Lithography. J PHOTOPOLYM SCI TEC 2016. [DOI: 10.2494/photopolymer.29.225] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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5
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Balderrama VS, Albero J, Granero P, Ferré-Borrull J, Pallarés J, Palomares E, Marsal LF. Design, fabrication and charge recombination analysis of an interdigitated heterojunction nanomorphology in P3HT/PC(70)BM solar cells. NANOSCALE 2015; 7:13848-59. [PMID: 26130048 DOI: 10.1039/c5nr02429c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
In this work interdigitated heterojunction photovoltaic devices were manufactured. A donor layer of P3HT nanopillars was fabricated by soft nanoimprinting using nanoporous anodic alumina templates. Subsequently, the PC70BM acceptor layer was deposited by spin coating on top of the P3HT nanopillars using a solvent that would not dissolve any of the previous material. Anisole solvent was used because it does not dissolve the bottom donor layer of nanopillars and provides a good wettability between the two materials. Charge extraction was used to determine the charge carrier densities n on the interdigitated heterojunction under operating conditions. Moreover, transient photovoltage measurements were used to find the recombination rate constant in combination with the charge carrier density. At the same time, the interdigitated structure was also compared with bulk heterojunction and bilayer solar cells manufactured with the same polymeric and fullerene materials in order to understand the recombination loss mechanisms in the ordered and disordered nanomorphologies of the active layers.
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Min SY, Kim TS, Lee Y, Cho H, Xu W, Lee TW. Organic nanowire fabrication and device applications. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2015; 11:45-62. [PMID: 25285601 DOI: 10.1002/smll.201401487] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Revised: 08/06/2014] [Indexed: 05/23/2023]
Abstract
Organic nanowires (ONWs) are flexible, stretchable, and have good electrical properties, and therefore have great potential for use in next-generation textile and wearable electronics. Analysis of trends in ONWs supports their great potential for various stretchable and flexible electronic applications such as flexible displays and flexible photovoltaics. Numerous methods can be used to prepare ONWs, but the practical industrial application of ONWs has not been achieved because of the lack of reliable techniques for controlling and patterning of individual nanowires. Therefore, an "individually controllable" technique to fabricate ONWs is essential for practical device applications. In this paper, three types of fabrication methods of ONWs are reviewed: non-alignment methods, massive-alignment methods, and individual-alignment methods. Recent research on electronic and photonic device applications of ONWs is then reviewed. Finally, suggestions for future research are put forward.
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Affiliation(s)
- Sung-Yong Min
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Republic of Korea
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Yang Y, Mielczarek K, Zakhidov A, Hu W. Efficient low bandgap polymer solar cell with ordered heterojunction defined by nanoimprint lithography. ACS APPLIED MATERIALS & INTERFACES 2014; 6:19282-19287. [PMID: 25295533 DOI: 10.1021/am505303a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this work, we demonstrate the feasibility of using nanoimprint lithography (NIL) to make efficient low bandgap polymer solar cells with well-ordered heterojunction. High quality low bandgap conjugated polymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) nanogratings are fabricated using this technique for the first time. The geometry effect of PCPDTBT nanostructures on the solar cell performance is investigated by making PCPDTBT/C70 solar cells with different feature sizes of PCPDTBT nanogratings. It is found that the power conversion efficiency (PCE) increases with increasing nanograting height, PCPDTBT/C70 junction area, and decreasing nanograting width. We also find that NIL makes PCPDTBT chains interact more strongly and form an improved structural ordering. Solar cells made on the highest aspect ratio PCPDTBT nanostructures are among the best reported devices using the same material with a PCE of 5.5%.
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Affiliation(s)
- Yi Yang
- Department of Materials Science and Engineering, ‡Department of Physics, §Department of Electrical Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States
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Yang Y, Mielczarek K, Aryal M, Zakhidov A, Hu W. Effects of nanostructure geometry on nanoimprinted polymer photovoltaics. NANOSCALE 2014; 6:7576-7584. [PMID: 24890562 DOI: 10.1039/c4nr01114g] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We demonstrate the effects of nanostructure geometry on the nanoimprint induced poly(3-hexylthiophene-2,5-diyl) (P3HT) chain alignment and the performance of nanoimprinted photovoltaic devices. Out-of-plane and in-plane grazing incident X-ray diffraction techniques are employed to characterize the nanoimprint induced chain alignment in P3HT nanogratings with different widths, spacings and heights. We observe the dependence of the crystallite orientation on nanostructure geometry such that a larger width of P3HT nanogratings leads to more edge-on chain alignment while the increase in height gives more vertical alignment. Consequently, P3HT/[6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) solar cells with the highest density and aspect ratio P3HT nanostructures show the highest power conversion efficiency among others, which is attributed to the efficient charge separation, transport and light absorption.
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Affiliation(s)
- Yi Yang
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, TX 75080, USA
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9
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Synthesis and properties of a new conjugated polymer containing benzodithiophene for polymer solar cells. Polym Bull (Berl) 2014. [DOI: 10.1007/s00289-014-1114-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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10
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Xu J, Asatekin A, Gleason KK. The design and synthesis of hard and impermeable, yet flexible, conformal organic coatings. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:3692-3696. [PMID: 22689327 DOI: 10.1002/adma.201201197] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Revised: 04/13/2012] [Indexed: 06/01/2023]
Abstract
A new design paradigm for conformal, all-organic coatings that retain their flexibility and chemical functionality while displaying exceptional mechanical hardness and barrier properties is presented. Initiated chemical vapor deposition is used to synthesize a novel alternating copolymer thin film. Upon annealing, films display elastic moduli exceeding 20 GPa, excellent scratch resistance and flexibility, and very low oxygen permeability.
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Affiliation(s)
- Jingjing Xu
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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11
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Yang Y, Mielczarek K, Aryal M, Zakhidov A, Hu W. Nanoimprinted polymer solar cell. ACS NANO 2012; 6:2877-92. [PMID: 22394246 DOI: 10.1021/nn3001388] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Among the various organic photovoltaic devices, the conjugated polymer/fullerene approach has drawn the most research interest. The performance of these types of solar cells is greatly determined by the nanoscale morphology of the two components (donor/acceptor) and the molecular orientation/crystallinity in the photoactive layer. A vertically bicontinuous and interdigitized heterojunction between donor and acceptor has been regarded as one of the ideal structures to enable both efficient charge separation and transport. Synergistic control of polymer orientation in the nanostructured heterojunction is also critical to improve the performance of polymer solar cells. Nanoimprint lithography has emerged as a new approach to simultaneously control both the heterojunction morphology and polymer chains in organic photovoltaics. Currently, in the area of nanoimprinted polymer solar cells, much progress has been achieved in the fabrication of nanostructured morphology, control of molecular orientation/crystallinity, deposition of acceptor materials, patterned electrodes, understanding of structure-property correlations, and device performance. This review article summarizes the recent studies on nanoimprinted polymer solar cells and discusses the outstanding challenges and opportunities for future work.
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Affiliation(s)
- Yi Yang
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States
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12
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Chen L, Sha WEI, Choy WCH. Light harvesting improvement of organic solar cells with self-enhanced active layer designs. OPTICS EXPRESS 2012; 20:8175-8185. [PMID: 22453487 DOI: 10.1364/oe.20.008175] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We present designs of organic solar cells (OSCs) incorporating periodically arranged gradient type active layer. The designs can enhance light harvesting with patterned organic materials themselves (i.e. self-enhanced active layer design) to avoid degrading electrical performances of OSCs in contrast to introducing inorganic concentrators into OSC active layers such as silicon and metallic nanostructures. Geometry of the OSC is fully optimized by rigorously solving Maxwell's equations with fast and efficient scattering matrix method. Optical absorption is accessed by a volume integral of the active layer excluding the metallic absorption. Our numerical results show that the OSC with a self-enhanced active layer, compared with the conventional planar active layer configuration, has broadband and wide-angle range absorption enhancement due to better geometric impedance matching and prolonged optical path. This work provides a theoretical foundation and engineering reference for high performance OSC designs.
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Affiliation(s)
- Luzhou Chen
- Department of Electrical and Electronic Engineering, the University of Hong Kong, Pokfulam Road, Hong Kong, China
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13
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Gong HJ, Kim JH, Yim SG. Carrier Gas Assisted Solvent Vapor Treatment for Surface Nanostructuring of Molecular Thin Films. B KOREAN CHEM SOC 2012. [DOI: 10.5012/bkcs.2012.33.3.825] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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14
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Kim J, Park CR, Yim S. Solvent spray method for simple fabrication of surface nanostructures of molecular thin films. RSC Adv 2012. [DOI: 10.1039/c1ra00348h] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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15
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Yang Y, Lee K, Mielczarek K, Hu W, Zakhidov A. Nanoimprint of dehydrated PEDOT:PSS for organic photovoltaics. NANOTECHNOLOGY 2011; 22:485301. [PMID: 22056527 DOI: 10.1088/0957-4484/22/48/485301] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We demonstrate the fabrication of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) nanogratings by a dehydration-assisted nanoimprint lithographic technique. Dehydration of PEDOT:PSS increases its cohesion to protect the nanostructures formed by nanoimprinting during demolding, resulting in the formation of high quality nanogratings of 60 nm in height, 70 nm in width and 70 nm in spacing (aspect ratio of 0.86). PEDOT:PSS nanogratings are used as hole transport and an electron blocking layer in blended poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-penyl-C61-butyric-acid-methyl-ester (PCBM) organic photovoltaic devices (OPV), showing enhancement of photocurrent and power efficiency in comparison to OPV devices with non-patterned PEDOT:PSS films.
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Affiliation(s)
- Y Yang
- Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
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Palacios R, Formentin P, Martinez-Ferrero E, Pallarès J, Marsal LF. β-Phase Morphology in Ordered Poly(9,9-dioctylfluorene) Nanopillars by Template Wetting Method. NANOSCALE RESEARCH LETTERS 2011; 6:35. [PMID: 27502658 PMCID: PMC3211439 DOI: 10.1007/s11671-010-9788-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Accepted: 09/09/2010] [Indexed: 05/23/2023]
Abstract
An efficient method based in template wetting is applied for fabrication of ordered Poly(9,9-dioctylfluorene) (PFO) nanopillars with β-phase morphology. In this process, nanoporous alumina obtained by anodization process is used as template. PFO nanostructures are prepared under ambient conditions via infiltration of the polymeric solution into the pores of the alumina with an average pore diameter of 225 nm and a pore depth of 500 nm. The geometric features of the resulting structures are characterized with environmental scanning electron microscopy (ESEM), luminescence fluorimeter (PL) and micro μ-X-ray diffractometer (μ-XRD). The characterization demonstrates the β-phase of the PFO in the nanopillars fabricated. Furthermore, the PFO nanopillars are characterized by Raman spectroscopy to study the polymer conformation. These ordered nanostructures can be used in optoelectronic applications such as polymer light-emitting diodes, sensors and organic solar cells.
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Affiliation(s)
- R Palacios
- Departament d'Enginyeria Electrónica, Eléctrica i Automática, Universitat Rovira i Virgili, Avda. Països Catalans 26, 43007, Tarragona, Spain
| | - P Formentin
- Departament d'Enginyeria Electrónica, Eléctrica i Automática, Universitat Rovira i Virgili, Avda. Països Catalans 26, 43007, Tarragona, Spain
| | - E Martinez-Ferrero
- Institute of Chemical Research of Catalonia (ICIQ), Avda. Països Catalans 16, 43007, Tarragona, Spain
| | - J Pallarès
- Departament d'Enginyeria Electrónica, Eléctrica i Automática, Universitat Rovira i Virgili, Avda. Països Catalans 26, 43007, Tarragona, Spain
| | - L F Marsal
- Departament d'Enginyeria Electrónica, Eléctrica i Automática, Universitat Rovira i Virgili, Avda. Països Catalans 26, 43007, Tarragona, Spain.
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Park JY, Hendricks NR, Carter KR. Solvent-assisted soft nanoimprint lithography for structured bilayer heterojunction organic solar cells. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:11251-11258. [PMID: 21749080 DOI: 10.1021/la201809g] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We introduce a novel method to easily fabricate nanopatterns at ambient conditions using solvent-assisted soft nanolithography. For this purpose, a P3HT/PCBM bilayer, one of well-known standard models of solar cell systems, was chosen to optimize bilayer solar cells using the new lithographic technique. The nanopatterns of P3HT made using this method have improved device efficiency compared to planar bilayer heterojunction of the solar cell. The new patterning process creates solar cell devices with a greater than 2-fold increase in power conversion efficiency (PCE) compared to an otherwise equivalent, flat device. This improvement in efficiency is due to the increased interfacial area created by the patterning process. This result demonstrates the feasibility of extensive applications toward nanolithography, relevant to device fabrication, such as electronic devices.
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Affiliation(s)
- Jin Young Park
- Polymer Science and Engineering, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, USA
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Lee JF, Hsu SLC, Lee PI, Chuang HY, Chen JS, Chou WY. Structure modification and annealing effect of polymer bulk heterojunction solar cells based on polyfluorene derivatives. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/pola.24905] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Xu Y, Zhang F, Feng X. Patterning of conjugated polymers for organic optoelectronic devices. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2011; 7:1338-1360. [PMID: 21520501 DOI: 10.1002/smll.201002336] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Indexed: 05/30/2023]
Abstract
Conjugated polymers have been attracting more and more attention because they possess various novel electrical, magnetical, and optical properties, which render them useful in modern organic optoelectronic devices. Due to their organic nature, conjugated polymers are light-weight and can be fabricated into flexible appliances. Significant research efforts have been devoted to developing new organic materials to make them competitive with their conventional inorganic counterparts. It is foreseeable that when large-scale industrial manufacture of the devices made from organic conjugated polymers is feasible, they would be much cheaper and have more functions. On one hand, in order to improve the performance of organic optoelectronic devices, it is essential to tune their surface morphologies by techniques such as patterning. On the other hand, patterning is the routine requirement for device processing. In this review, the recent progress in the patterning of conjugated polymers for high-performance optoelectronic devices is summarized. Patterning based on the bottom-up and top-down methods are introduced. Emerging new patterning strategies and future trends for conventional patterning techniques are discussed.
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Affiliation(s)
- Youyong Xu
- College of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, PR China
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20
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Bearden SD, Cannon JP, Gold SA. Solvent Effects on Template Wetting Nanofabrication of MEH-PPV Nanotubules. Macromolecules 2011. [DOI: 10.1021/ma101958q] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Steven D. Bearden
- Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana 71272, United States
| | - Joseph P. Cannon
- Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana 71272, United States
| | - Scott A. Gold
- Chemical and Materials Engineering Department, University of Dayton, Dayton, Ohio 45469, United States
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Farinhas J, Ferreira Q, Di Paolo RE, Alcácer L, Morgado J, Charas A. Nanostructured donor/acceptor interfaces in photovoltaic cells using columnar-grain films of a cross-linked poly(fluorene-alt-bithiophene). ACTA ACUST UNITED AC 2011. [DOI: 10.1039/c1jm10195a] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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Tomohiro K, Hoto N, Kawata H, Hirai Y. Fine Pattern Transfer of Functional Organic Polymers by Nanoimprint. J PHOTOPOLYM SCI TEC 2011. [DOI: 10.2494/photopolymer.24.71] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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23
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Ko DH, Tumbleston JR, Gadisa A, Aryal M, Liu Y, Lopez R, Samulski ET. Light-trapping nano-structures in organic photovoltaic cells. ACTA ACUST UNITED AC 2011. [DOI: 10.1039/c1jm12300a] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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25
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Kim JK, Lee DE, Lee WI, Suh KY. Measurement of pull-off force on imprinted nanopatterns in an inert liquid. NANOTECHNOLOGY 2010; 21:295306. [PMID: 20601765 DOI: 10.1088/0957-4484/21/29/295306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We report on the measurement of the pull-off force on nanoscale patterns that are formed by thermal nanoimprint lithography (t-NIL). Various patterns with feature sizes in the range of 50-900 nm were fabricated on silicon substrates using a rigiflex polymeric mold of ultraviolet curable polyurethane acrylate (PUA, Young's modulus approximately 1 GPa) or perfluoropolyether (PFPE, Young's modulus approximately 10.5 MPa) and a resist layer of polystyrene (PS) of three different molecular weights (M(w) = 18,100, 211,600 and 2043,000). The pull-off force was measured in non-polar, non-reactive perfluorodecalin (PFD) solvent between a sharp atomic force microscopy (AFM) tip and an imprinted pattern. Our experimental data demonstrated that the measured pull-off forces were in good agreement with a simple adhesion model based on Lifshitz theory. Also, the force on the pressed region (valley) is higher than that on the cavity region (hill), with the ratio (hill/valley) decreasing with the decrease of pattern size and the increase of molecular weight. The confinement effects were more pronounced for smaller patterns (<300 nm) and higher molecular weights (M(w) = 211,600 and 2043,000) presumably due to sluggish movement of polymer chains into nano-cavities. Finally, the experimental observations were compared with molecular dynamic simulations based on a simplified amorphous polyethylene model.
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Affiliation(s)
- Jae Kwan Kim
- School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea
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Liang X, Chen T, Jung YS, Miyamoto Y, Han G, Cabrini S, Ma B, Olynick DL. Nanoimprint-induced molecular stacking and pattern stabilization in a solution-processed subphthalocyanine film. ACS NANO 2010; 4:2627-2634. [PMID: 20411983 DOI: 10.1021/nn100075t] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We present a systematic study on the thermal nanoimprinting of a boron subphthalocynamine molecule, 2-allylphenoxy-(subphthalocyaninato)boron(III) (SubPc-A), which represents a class of attractive small-molecular weight organic compounds for organic-based photovoltaics (OPV). The final equilibrium imprinted feature profile strongly depends on the imprinting temperature. The highest feature aspect ratio (or contrast) occurs at a specific window of imprinting temperatures (80-90 degrees C). X-ray diffraction indicates that the nanoimprint at such a temperature window can induce high-degree molecular stacking, which can help stabilize the imprinted features. Outside this window, we observed a pronounced relaxation of imprinted features after template removal, which is attributed to the surface diffusion. Key factors affecting the final equilibrium profile of the imprinted features were simulated. From the simulation, it was found that the crystallization-induced anisotropy of surface energy stabilized imprinted features. Simulated parameters such as stable feature aspect ratio and pitch agree well with experimental data. Such work provides an important guideline for optimizing the nanopatterning of small-molecular-weight organic compounds.
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Affiliation(s)
- Xiaogan Liang
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA.
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Chung SH, Son SJ, Min J. The nanostructure effect on the adhesion and growth rates of epithelial cells with well-defined nanoporous alumina substrates. NANOTECHNOLOGY 2010; 21:125104. [PMID: 20195010 DOI: 10.1088/0957-4484/21/12/125104] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We systematically analyzed the adhesion and the proliferation of cells on various nanoporous alumina surfaces to understand the effects of nanostructured surfaces on cell behavior. Various nanoporous surfaces were fabricated using the anodizing method and characterized by atomic force microscopy and scanning electron microscopy. The adhesion rate and proliferation rate of cells as functions of pore size and depth were statistically investigated using a colorimetric method. The adhesion rate of cells was not affected by the depth of the nanoporous surface whereas the proliferation of cells dramatically increased when the aspect ratio of the nanopore was near unity. This phenomenon was further verified by comparing the change in roughness of the cytoplasmic layer of cells adhered on a nanoporous surface with that of a bare nanoporous surface. The proliferation of cells was also influenced by the pore size of the nanoporous surface because the nanostructure could control the interaction between extracellular matrix (ECM) molecules and the surface. In conclusion, the nanostructured surfaces affected cell adhesion and proliferation by increasing the surface area to which the cells could adhere, and the interactions between small ECM molecules were influenced by the sufficiently small structures of the nanosurface.
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Affiliation(s)
- S H Chung
- Department of Chemical and Biomolecular Engineering, Sogang University, Seoul, Korea
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28
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Heremans P, Cheyns D, Rand BP. Strategies for increasing the efficiency of heterojunction organic solar cells: material selection and device architecture. Acc Chem Res 2009; 42:1740-7. [PMID: 19751055 DOI: 10.1021/ar9000923] [Citation(s) in RCA: 173] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Thin-film blends or bilayers of donor- and acceptor-type organic semiconductors form the core of heterojunction organic photovoltaic cells. Researchers measure the quality of photovoltaic cells based on their power conversion efficiency, the ratio of the electrical power that can be generated versus the power of incident solar radiation. The efficiency of organic solar cells has increased steadily in the last decade, currently reaching up to 6%. Understanding and combating the various loss mechanisms that occur in processes from optical excitation to charge collection should lead to efficiencies on the order of 10% in the near future. In organic heterojunction solar cells, the generation of photocurrent is a cascade of four steps: generation of excitons (electrically neutral bound electron-hole pairs) by photon absorption, diffusion of excitons to the heterojunction, dissociation of the excitons into free charge carriers, and transport of these carriers to the contacts. In this Account, we review our recent contributions to the understanding of the mechanisms that govern these steps. Starting from archetype donor-acceptor systems of planar small-molecule heterojunctions and solution-processed bulk heterojunctions, we outline our search for alternative materials and device architectures. We show that non-planar phthalocynanines have appealing absorption characteristics but also have reduced charge carrier transport. As a result, the donor layer needs to be ultrathin, and all layers of the device have to be tuned to account for optical interference effects. Using these optimization techniques, we illustrate cells with 3.1% efficiency for the non-planar chloroboron subphthalocyanine donor. Molecules offering a better compromise between absorption and carrier mobility should allow for further improvements. We also propose a method for increasing the exciton diffusion length by converting singlet excitons into long-lived triplets. By doping a polymer with a phosphorescent molecule, we demonstrate an increase in the exciton diffusion length of a polymer from 4 to 9 nm. If researchers can identify suitable phosphorescent dopants, this method could be employed with other materials. The carrier transport from the junction to the contacts is markedly different for a bulk heterojunction cell than for planar junction cells. Unlike for bulk heterojunction cells, the open-circuit voltage of planar-junction cells is independent of the contact work functions, as a consequence of the balance of drift and diffusion currents in these systems. This understanding helps to guide the development of new materials (particularly donor materials) that can further boost the efficiency of single-junction cells to 10%. With multijunction architectures, we expect that efficiencies of 12-16% could be attained, at which point organic photovoltaic cells could become an important renewable energy source.
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Affiliation(s)
| | - David Cheyns
- IMEC v.z.w., Kapeldreef 75, B-3001 Leuven, Belgium
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Aryal M, Trivedi K, Hu WW. Nano-confinement induced chain alignment in ordered P3HT nanostructures defined by nanoimprint lithography. ACS NANO 2009; 3:3085-90. [PMID: 19731931 DOI: 10.1021/nn900831m] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/14/2023]
Abstract
Control of polymer morphology and chain orientation is of great importance in organic solar cells and field effect transistors (OFETs). Here we report the use of nanoimprint lithography to fabricate large-area, high-density, and ordered nanostructures in conjugated polymer poly(3-hexylthiophene) or P3HT, and also to simultaneously control 3D chain alignment within these P3HT nanostructures. Out-of-plane and in-plane grazing incident X-ray diffraction were used to determine the chain orientation in the imprinted P3HT nanostructures, which shows a strong dependence on their geometry (gratings or pillars). Vertical chain alignment was observed in both nanogratings and nanopillars, indicating strong potential to improve charge transport and optical properties for solar cells in comparison to bulk heterojunction structure. For P3HT nanogratings, pi-pi stacking along the grating direction with an angular distribution of +/-20 degrees was found, which is favorable for OFETs. We propose the chain alignment is induced by the nanoconfinement during nanoimprinting via pi-pi interaction and hydrophobic interaction between polymer chain and mold surfaces.
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Affiliation(s)
- Mukti Aryal
- Department of Electrical Engineering, The University of Texas at Dallas, Richardson, Texas, USA
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30
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Hsu SLC, Lin YC, Lee RF, Sivakumar C, Chen JS, Chou WY. Synthesis and characterization of new low bandgap polyfluorene copolymers for bulk heterojunction solar cells. ACTA ACUST UNITED AC 2009. [DOI: 10.1002/pola.23582] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Charas A, Ferreira Q, Farinhas J, Matos M, Alcácer L, Morgado J. Insoluble Patterns of Cross-Linkable Conjugated Polymers from Blend Demixing in Spin Cast Films. Macromolecules 2009. [DOI: 10.1021/ma901329n] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Ana Charas
- Instituto de Telecomunicações, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
| | - Quirina Ferreira
- Instituto de Telecomunicações, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
| | - Joana Farinhas
- Instituto de Telecomunicações, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
- Dep. Eng. Química, Instituto Superior de Engenharia de Lisboa, Lisbon, Portugal
| | - Manuel Matos
- Instituto de Telecomunicações, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
- Dep. Eng. Química, Instituto Superior de Engenharia de Lisboa, Lisbon, Portugal
| | - Luís Alcácer
- Instituto de Telecomunicações, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
- Dep. Eng. Química e Biológica, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
| | - Jorge Morgado
- Instituto de Telecomunicações, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
- Dep. Eng. Química e Biológica, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049-001, Lisbon, Portugal
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Park HJ, Kang MG, Guo LJ. Large area high density sub-20 nm SiO(2) nanostructures fabricated by block copolymer template for nanoimprint lithography. ACS NANO 2009; 3:2601-8. [PMID: 19708638 DOI: 10.1021/nn900701p] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We developed simple fabrication methods to effectively transfer the block copolymer nanopatterns to a substrate material. High aspect ratio, sub-20 nm nanopillar and nanohole structures are successfully fabricated in a SiO(2) layer in large area format, and the versatile utilities of these nanostructures as nanoimprint molds are studied. Nanoimprint lithography using these molds makes it possible to easily replicate densely packed block copolymer nanotemplate patterns on arbitrary substrates in a short processing time by using a large variety of polymer materials, including functional materials such as conjugated polymers. In addition, the PDMS soft stamps with both nanohole and nanopillar pattern polarities, which are useful tools for soft lithography and transparent template applications, are also successfully fabricated using the pillar- and hole-type SiO(2) molds. These soft stamps provide an effective way to fabricate controllable as well as reproducible plasmonic metal nanostructures with tunable surface plasmon resonances.
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Affiliation(s)
- Hui Joon Park
- Macromolecular Science and Engineering, The University of Michigan, Ann Arbor, Michigan 48109, USA
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